There are a number of methods known in the art of providing heat in a cooktop. One preferred method is to use a gas burner which is able to deliver high levels of heating and which responds fairly quickly to desired changes in level. An example of a typical gas burner is described in WO 01/50065. It is typical that the finest level of control will be desired at the lower levels of output range for various cooking duties. In order to achieve good level control, various fuel gas flow control valves have been proposed such as those described in U.S. Pat. No. 5,009,393 and WO 01/33118.
In a typical gas cooktop a trivet is provided to support a cooking vessel above the gas burner and attempts have been made previously to accommodate various shapes of cooking vessels. Examples of trivet arrangements are described in U.S. Pat. No. 6,588,417, WO 02/066899 and U.S. Pat. No. 5,819,719. For gas cooktops, the combustion of fuel gases requires clearance under the cooking vessel to allow flow of the combustion and exhaust gases, which is provided by a trivet to support the cooking vessel the correct distance above the gas flame. A trivet is usually constructed of cast iron or enamel coated steel and comprises a number of narrow prongs to limit interference with the flame and upon which the cooking vessel may rest in a horizontal plane.
Trivets and burner components comprise many complex shapes and surfaces which can make cleaning more difficult. These structures are also visually complex. Il order to aid with cleaning, it is known to provide gas heating appliances having removable trivets and removable burner components. However in some cases it may be possible for a user to re-assemble these components incorrectly, which can lead to instability of the cooking vessel and/or incorrect operation of the burner. Incorrect assembly or operation of the gas cooktop components may be hazardous.
Further, various constructions of gas burners and burner rings are also disclosed in the prior art. Prior art burners generally have flame outlet openings which are formed as slots, grooves or bore holes which are generally directed outwardly in approximately a radial direction. Fuel gas is supplied through the burner body and exits through the burner ports where it is combusted forming a ring of flames which are used to heat cooking vessels. The efficiency of conventional gas burners is limited by the need to maintain sufficient clearance around the burner head to allow the flame to draw in enough of the surrounding air to achieve complete combustion of the fuel gas. Due to the clearance between the burner head and the cooking vessel, much of the flame has passed the hottest phase of combustion by the time it contacts the surface of the cooking vessel. Much of the flame heat diffuses into the surrounding mass of flowing gases such that the temperature difference between these flowing gases and the surface of the pot is reduced, which in turn reduces the rate of heat transfer to the cooking vessel.
The operating range of conventional cooktop gas burners is limited to the performance range of the venturi and the burner ports. The venturi uses the velocity of the fuel gas flowing through a small orifice to draw in an approximately proportional volume of air as required for primary combustion. The fixed geometry of the venturi and fuel gas jet limit the range over which this type of burner will operate. Similarly, the range of operation of burner ports is a function of their cross sectional area and the ability of flame to stay attached to the burner port against the flow of the gases when the burner is at the upper end of its operating range. For these prior art burners, burn back velocity and heat transfer between the flame and the burner head provides the lower limit of the operating range of the port structure by extinguishing the flame.